I’ve set it to include only search results from specific categories, and yet, it’s still showing search results from all categories. What am I doing wrong?
Based on your screenshot, I would suggest only adding the ‘Books’ category, since all the sub-categories are also included, and it is redundant.
The search will still include results, which does not belong to any other categories, or does not have any connection with the given taxonomy. To avoid that, make sure to also turn OFF this option.
That should do the trick.